Abstract: In order to study the shear-flow coupling characteristics of joints under constant normal stiffness (CNS) boundary condition, the shear-flow coupling tests under three different stiffness and seepage pressure settings were carried out for duplicate joint specimens with three different joint roughnesses. Meanwhile, the effects of normal stiffness, seepage pressure and joint roughness on the mechanical properties and seepage characteristics in joint shearing process were systematically analyzed. The test results indicate that the peak shear strength of joint increases with the increasing of normal stiffness, while the flow rate, equivalent hydraulic aperture and transmissivity decrease with the increasing of normal stiffness; and the flow rate of seepage through joint surfaces decreases during shearing process with the increasing of joint roughness. Similar to the three-stage change rule of joint dilatancy, three distinct stages are also observed for the flow rate, equivalent hydraulic aperture and transmissivity: rapid growth stage, slow growth stage, and stable stage. During the stable stage, the flow rate has approximately a linear relation with the variations of the normal stiffness and seepage pressure. The joints with higher roughness present lower flow rate as the seepage pressure increases.

Key words: joints, shear-seepage coupling behaviour, normal stiffness, seepage pressure, joint roughness